1. Technical Field
The present invention relates to a method of forming a high dielectric film used in a semiconductor device and a method of manufacturing a capacitor, and more particularly, to a method of forming a high dielectric film using atomic layer deposition (ALD) and a method of manufacturing a capacitor having the high dielectric film.
2. Description of the Related Art
As the integration density and capacitance of semiconductor devices have increased, there have been intensive studies on formation of gate insulating films or capacitor dielectric films of MOSFETs using high dielectric materials. When a high dielectric film is formed as a gate insulating film, since the high dielectric film having the same equivalent oxide thickness (Toxeq) as an SiO2 film has a greater thickness than the SiO2 film, a rapid increase in leakage current due to tunneling of electrons can be reduced. For example, when an SiO2 film is used as a gate insulating film, if the SiO2 film has a thickness of 15 Å or less, a leakage current dramatically increases due to tunneling. However, when the gate insulating film is formed of a high dielectric material such as HfO2, ZrO2, Ta2O5, or TiO2, even if the high dielectric film has the same equivalent oxide thickness (Toxeq) as the SiO2 film, a rapid increase in leakage current can be prevented.
However, when a gate insulating film of a MOSFET device is formed of a high dielectric film, some problems are generated. For example, when a gate insulating film is formed of a high dielectric material such as HfO2 or ZrO2, dopant diffusion of B, P, or As from an upper polysilicon gate electrode lowers carrier mobility in channels. Also, a high dielectric film formed of HfO2 may be easily crystallized by a subsequent annealing process, thus causing current leakage. Accordingly, to form a gate insulating film using a high dielectric material, dopant diffusion from the upper polysilicon gate electrode should be suppressed, and thermal stability should be secured during an annealing process.
To prevent dopant diffusion and secure thermal stability, research for obtaining a high dielectric oxynitride film, such as an HfON film and a ZrON film, by adding nitrogen to a high dielectric oxide film, such as an HfO2 film or a ZrO2 film, has progressed. If the high dielectric oxynitride film is formed by adding nitrogen to the high dielectric oxide film, such as the HfO2 film or the ZrO2 film, diffusion of impurities from an upper electrode can be prevented, and thermal stability can be ensured by raising the crystallization temperature of the high dielectric film. To form the oxynitride film, such as the HfON film and the ZrON film, an oxide film, such as an HfO2 film or a ZrO2 film, can be deposited and annealed in an atmosphere of NH3 or N2O. However, this method cannot easily obtain a desired profile of nitrogen in a thin film formed of HfO2 or ZrO2, and should include an additional N2-annealing process after the oxide film is deposited.
To form a high dielectric oxynitride film, a method of depositing an HfON film by ALD using a new Hf precursor containing nitrogen has been developed. However, since N—C coupling in the N-containing precursor, such as Hf[N(CH3)2]4, is very great, even if an HfON film is deposited using an oxidizer such as H2O, carbon remains in the HfON film. The remaining carbon degrades the electrical characteristics of the HfON film.
FIG. 1 is a graph of current density versus applied voltage in a metal oxide semiconductor (MOS) transistor that uses a conventional HfON film formed by ALD as a gate insulating film. In FIG. 1, a solid curve corresponds to an HfON film as deposited, and a dotted curve corresponds to an HfON film that has been annealed in an atmosphere of N2 at a temperature of about 800° C. Both films are formed by ALD using a precursor of Hf[N(CH3)2]4 and an oxidizer of H2O at a temperature of about 300° C. Each of the HfON films is formed by repeatedly supplying the precursor Hf[N(CH3)2]4, purging a reactor, supplying the oxidizer H2O, and purging the reactor several times.
Referring to FIG. 1, the conventional HfON film deposited using ALD (the solid curve) exhibited a degraded leakage current characteristic. Specifically, when the applied voltage was −2V, the density of the leakage current was about 0.5 A/cm2. Even when the HfON film was annealed in an atmosphere of N2 at a temperature of about 800° C., the leakage current characteristic of the HfON film did not improve significantly. This is because the conventional HfON film contained a considerable amount of carbon or had numerous defects.
FIG. 2 is a graph showing a TOF-secondary ion mass spectrometer (TOF-SIMS) analysis of a conventional HfON film deposited using ALD. The TOF-SIMS analysis is employed for the qualitative and quantitative analysis of elements. Referring to FIG. 2, the conventional HfON formed by ALD contains a large amount of carbon, which degrades the leakage current characteristic of the HfON thin film. FIG. 3 is a graph showing a TOF-SIMS analysis of a conventional HfON film deposited by ALD and then annealed. As can be seen from FIG. 3, even if annealed, the HfON film still contains a large amount of carbon. Thus, the electrical characteristics of the HfON film are degraded. As a result, when the HfON film is formed by ALD using the precursor Hf[N(CH3)2]4, although dopant diffusion can be prevented by the N-containing precursor, a thin film characteristic is degraded since the amount of carbon in the HfON film increases. Also, the carbon in the HfON film cannot be removed by an additional annealing process.
Meanwhile, with the increasing integration density of semiconductor devices, while the capacitance of a capacitor per cell required for stable driving of devices remains constant, the area of each cell that is available for the capacitor decreases. Thus, the integration density of semiconductor devices is reaching a technical limit. To overcome the technical limit, increasing the electric charge per cell by increasing the capacitance of the capacitor is needed. The capacitance of the capacitor can be increased by raising the dielectric constant of a capacitor dielectric film. Techniques of replacing a conventional SiO2 film having a dielectric constant of about 3.9, a Si3N4 film having a dielectric constant of about 7.2, or an ONO film having a dielectric constant of about 3.9-7.2, by a high dielectric film have been developed.
Substitutable high dielectric film candidates include a Ta2O5 film having a dielectric constant of 20-60, an HfO2 film having a dielectric constant of about 20, a TiO2 film having a dielectric constant of about 40, an Al2O3 film having a dielectric constant of about 10, an La2O3 having a dielectric constant of about 20, and ferroelectric combination films, such as PZT, PLZT, BST, and STO, whose dielectric constants range from several tens to several hundreds. However, all of these high dielectric films cannot necessarily be applied to semiconductor devices. Whether or not a new dielectric material can be applied to a semiconductor device is determined in consideration of suitableness to conventional semiconductor fabrication, stability of electrode patterns and etching processes, stability of device fabrication, mass production, economic efficiency, and stability of device operation.
A dielectric film can be deposited using various methods, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), or atomic layer deposition (ALD). When a capacitor having a 3-dimensional lower electrode is formed, the dielectric film is preferably formed using CVD or ALD. The CVD or ALD process requires precursors and oxidizers. A high dielectric film can be deposited using: (1) a precursor, for example, metal halides, such as metal chlorides, and metal organic (MO) sources, such as metal alkoxides and metal β-diketonates; and (2) an oxidizer, such as O2, O3, or H2O.
In the CVD method, thin films are formed by simultaneously supplying source gases for forming films, such as the precursors and oxidizers, to reactors. However, in the ALD method, the source gases for forming films are not simultaneously supplied, but are supplied in pulses by time division, and every step of supplying a source gas is directly followed by a purge step using an inert gas, so that the remaining gas or by-products are removed.
For example, after a precursor is supplied to a reactor, if the reactor is purged by supplying an inert gas as a purging gas, while a thin chemisorbed precursor remains on a wafer on the atomic-size level, other precursors are exhausted from the reactor. In this state, if an oxidizer is supplied to the reactor, the oxidizer reacts with the precursor remaining on the wafer, thus generating a thin dielectric film or metal oxide film on the near-atomic level. Thereafter, the reactor is purged to remove a physisorbed oxidizer or by-products. As described above, a process including supplying a precursor, purging a reactor, supplying an oxidizer, and purging the reactor is called one cycle of ALD, and a resulting film can be formed to a desired thickness by controlling the number of cycles. It is known that the ALD method is superior to the CVD method in that the ALD method can produce films with good characteristics and good step coverage for a 3-dimensional structure, and can easily control the thickness of a thin dielectric film. Accordingly, as design rules for semiconductor devices such as DRAMs decrease, it is preferable to form a high dielectric film using ALD.
When a high dielectric film is deposited using ALD, it is preferable to form a combination film formed of several high dielectric materials rather than a single film formed of a certain high dielectric material, considering dielectric characteristics. Normally, any single film formed of a certain high dielectric material has some defects. For example, an HfO2 film, which has a dielectric constant of about 20 and is formed by ALD, is easily crystallized at a temperature of only about 400° C. If the HfO2 film is crystallized, after a capacitor is manufactured, a leakage current flows between crystal grains to deteriorate the electrical characteristics of the capacitor. For this reason, a high dielectric film formed by ALD is required to have a high dielectric constant and also remain amorphous at a relatively high temperature.
To form an amorphous high dielectric film using ALD, in a first method, a combination film can be formed by laminating two different kinds of high dielectric oxide films. For example, an Al2O3 film and an HfO2 film can be laminated using ALD to form a combination film. Although the Al2O3 film has a lower dielectric constant than the HfO2 film, since the crystallization temperature of the Al2O3 film is higher than 900° C., the resulting combination film is not crystallized during typical semiconductor processes. The dielectric constant and crystallization of the combination film that is formed by laminating the Al2O3 film and the HfO2 film depend on a ratio of Al to Hf in the combination film. That is, if a ratio of Hf to Al+Hf increases, the dielectric constant and crystallization of the combination film increase, and if a ratio of Al to Hf+Al increases, the dielectric constant and crystallization thereof decrease. Korean Patent Laid-open Publication No. 2001-0063452 proposes a method of alternately laminating a Ta2O5 film and a TiO2 film using ALD and converting the stack film of Ta2O5 and TiO2 into a single compound film by a subsequent annealing process.
Secondly, an amorphous high dielectric film can be formed using ALD by adding nitrogen to a high dielectric material. For example, an HfO2 film is deposited using ALD and annealed in an N2 atmosphere, thereby forming an HfON film. Although the HfON film has a slightly lower dielectric constant than an HfO2 film, the crystallization temperature of the HfON film is higher than that of the HfO2 film. Thus, the HfON film can retain more stable leakage current characteristics than the HfO2 film. Also, as described above, the nitrogen contained in the HfON film prevents diffusion of impurities from upper and lower electrodes, and thus the HfON film can be a stable dielectric film. However, a desired profile of nitrogen in the HfON film cannot be easily obtained by N2-annealing, and a subsequent nitridation process is required. Thus, Korean Patent Laid-open Publication No. 2000-0013654 discloses a method of forming an AlON film by annealing an AlN film, which is formed using ALD, in an O2 atmosphere.
Thirdly, an amorphous high dielectric film, which is formed using ALD, can be a combination film formed of three or more elements. For example, an HfON film and an AlON film are laminated using ALD, thereby forming a combination film formed of HfON/AlON. It is expected that this combination film has the advantages of both the foregoing stack film of HfO2 and Al2O3, and an HfON film. That is, by adding nitrogen to the combination oxide film, the resulting high dielectric film can function as a barrier to diffusion of impurities and retain a high dielectric constant and high crystallization temperature with only a small concentration of Al. Korean Patent Laid-open Publication No. 2002-0002156 discloses a method of laminating TiO2 and TaON using ALD and forming a combination film of TaON and TiO2 by a subsequent annealing process. As it is difficult to form a desired high dielectric combination film by CVD, the ALD method is preferred here. When the combination film is deposited using ALD, a combination film having a desired thickness and composition can be formed by controlling the order in which source gases are supplied and the number of cycles.
However, since the method of forming a high dielectric combination film using ALD includes many steps of supplying gases along with purge steps, the method impedes the mass production of semiconductor devices. For instance, when a combination film is formed of a stack film of HfON and AlON, exceedingly numerous processes should be performed, such as supplying HfCl4 as an Hf source gas, purging a reactor, supplying O2, purging the reactor, N2-annealing, supplying trimethyl aluminum (TMA) as an Al source gas, purging the reactor, supplying O2, purging the reactor, and N2-annealing, thus inhibiting mass production.
Thus it would be desirable to provide a method of forming a high dielectric film using ALD that improves a leakage current characteristic of the high dielectric film by reducing defects such as carbon and precisely controls the amount of nitrogen in the high dielectric film.
It would also be desirable to provide a method of forming a high dielectric combination film using ALD that facilitates mass production, precisely controls the composition and the thickness of the high dielectric combination film, and retains a stable leakage current characteristic.
It would further be desirable to provide a method of manufacturing a capacitor including the high dielectric combination film formed by either of the foregoing methods.
According to one aspect of the present invention, there is provided a method of forming a high dielectric film using atomic layer deposition, comprising (a) supplying a precursor containing a metal element to a semiconductor substrate and purging a reactor; (b) supplying an oxidizer and purging the reactor; and (c) supplying a reaction source containing nitrogen and purging the reactor. Step (c) can be performed before or after step (b). Step (b) and step (c) can be performed at the same time. After performing step (c), the method can further comprise supplying an oxidizer and purging the reactor.
The precursor containing the metal element can be an Hf precursor formed of a combination of Hf and one of O, C, H, and N, and the high dielectric film can be an HfON film. The Hf precursor can be one selected from the group consisting of Hf[N(CH3)2]4, Hf[N(C2H5)2]4, and Hf[N(C2H5)CH3]4.
The oxidizer can be one selected from the group consisting of O3, H2O, H2O2, CH3OH, C2H5OH, and C3H7OH. The reaction gas containing the nitrogen can be one selected from the group consisting of NH3 gas, N2O gas, NO gas, and NH3 plasma.
The high dielectric film can be one selected from the group consisting of N-augmented ZrO2, N-augmented ZrON, N-augmented Al2O3, N-augmented Ta2O5, N-augmented TiO2, N-augmented SrTiO3, N-augmented TiAlO, N-augmented HfAlO, N-augmented HfTiO, and a combination thereof. The precursor can be combined with one of O, C, H, and N.
The high dielectric film can be used as a gate insulating film of a semiconductor device. The high dielectric film can be used as a capacitor dielectric film.
According to another aspect of the present invention, there is provided a method of forming a high dielectric film on a semiconductor substrate using atomic layer deposition, comprising (a) supplying a first reaction source containing a first metal element and purging a reactor; (b) supplying a second reaction source containing a second metal element and purging the reactor, the second metal element being different from the first metal element; (c) supplying a third reaction source containing N; and (d) supplying an oxidizer and purging the reactor.
After performing step (b), the method can further comprise supplying the first reaction source and purging the reactor.
After performing step (d), the method can further comprise performing an annealing process to density the high dielectric film. The annealing process can be performed in an atmosphere of one selected from the group consisting of O2, O3, N2O, Ar, N2, H2, He, NH3, and a combination thereof, at a temperature of room temperature to 600° C., under a pressure of about 0.1 to 760 Torr.